Fluid streams, such as air streams, often carry contaminant material. In many instances, it is desirable to filter some or all of the contaminant material from the fluid streams. For example, particulate contaminants can be carried by air streams into internal combustion engines for motorized vehicles or for power generation equipment. It is preferred for such systems that selected contaminant material, such as particulate contaminants, be removed from, or have its level reduced in, the air stream. Also liquid streams in the engine lubrication systems, hydraulic systems, coolant systems, and fuel systems, can carry particulate contaminant that should be filtered. It is preferred for such systems that the fluid streams are free from select contaminant material or have the level of contaminant material therein reduced. A variety of fluid filter arrangements (air or liquid filter) have been developed for contaminant reduction.
Many filter arrangements include pleated or folded filtration media. Pleated or folded filtration media packs have a tendency to be non-self-supporting. Typically, some type of structure is used to support or stabilize the pleats of the pleated media pack. Furthermore, the filter media density of a pleated filtration media pack typically refers to the number of pleat faces per unit distance, and is often limited to reduce the occurrence of pleat faces contacting each other. Pleat faces that contact each other have a tendency to create masking or loss of filtration media effectiveness at the areas of contact. Exemplary pleated filtration media packs are disclosed, for example, in U.S. Pat. Nos. 8,216,335; 6,652,614; 8,603,210; 7,070,642; 4,963,171; and 5,125,941.
Another type of filtration media pack provided to address some of the shortcomings of pleated filtration media packs are referred to as fluted filtration media packs or z-filtration media packs. Exemplary z-filtration media packs are disclosed in, for example, U.S. Pat. Nos. 5,562,825; 5,049,326; 5,895,574; and 4,925,561. Such z-filtration media packs typically include alternating fluted media sheet and facing media sheet, and form a first flow face and a second flow face. While z-filtration media packs tend to be self-supporting and can provide for increased media density relative to certain pleated filtration media arrangements, z-filtration media packs have a tendency to suffer from masking at the locations where the fluted media sheet contacts the facing media sheet.
Continued improvement in the design of filtration media packs and filter elements is desired in order to provide improved properties including contaminant loading, longevity, compactness, media density, and fluid flow properties.